TOKYO—A team from the International Atomic Energy Agency on Monday began its review of Japan’s plan to begin releasing more than a million tons of treated radioactive water into the sea from the wrecked Fukushima nuclear plant—a review that Japan hopes will instill confidence in the plan. The 15-member team is to visit the Fukushima plant on Tuesday and meet with government and utility officials during its five-day mission. The government and Tokyo Electric Power Company Holdings announced plans last year to begin gradually releasing the still-contaminated water in spring 2023 after its further treatment and dilution. The water is being stored in about 1,000 tanks at the damaged plant which officials say need to be removed so the reactors can be decommissioned. The tanks are expected to reach their capacity of 1.37 million tons later this year. A massive earthquake and tsunami in 2011 destroyed the Fukushima plant’s cooling …